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Question of the Week



Permalink How do I go about converting unmanaged pasture to organic cropland?

B.P.
South Dakota

Answer:

I am pleased to provide you with information on converting unmanaged pasture into organic corn or oats.

This year you might think about putting the field into hay barley. It can be planted at about 100 pounds per acre, or you could interseed annual ryegrass with it at a rate of 60 to 75 pounds of barley and 15 pounds of annual ryegrass per acre and have some good late summer grazing that will extend into the fall, if you have livestock on your farm. After you take off the hay barley, the ryegrass will tiller and provide good soil cover and grazing. If you choose not to graze it, you could mow it just after flowering prior to seed set. Annual ryegrass comes back well from seed, so its best to manage it such that it does not go to seed.

Another intercrop you could use would be buckwheat planted into the barley. The summer growing buckwheat will come back after cutting the barley in mid summer and provide an excellent summer cover crop that can be incorporated into the soil in the fall in preparation for planting a winter cover crop. Consider winter peas as a winter cover crop. They will likely winter kill and make way for spring oat planting. If corn will be planted next year, winter rye and red clover or vetch would be a good choice of winter cover crop as they do not winter kill as easily as peas, and can be mowed in the spring. The corn can be no-till planted directly in to the stubble.

The main thing is to (1) get the soil covered with a plant that you can easily manage, like an annual grass or legume (or both), (2) choose a plant that will not compete with your cash crop, and (3) take advantage of soil-building characteristics of cover crops and intercrops. See below for more information on cover crops and intercropping.

Cover Crops

Using annual legumes (such as clovers, winter peas, and vetch) and annual grasses (such as rye, oats, or annual ryegrass) as a cover crop in row crops provides necessary soil cover, improved soil tilth (by increasing humus or organic matter), added nitrogen from legume nodulation, soil moisture retention, and increased biodiversity which in turn increases food and cover for beneficial organisms, including insect predators and pollinators.

The main purpose of a cover crop of course is to cover the soil. Therefore overall plant biomass production is a key consideration when selecting a planting method. High amounts of clover biomass can be obtained with either a 6 or 12 inch row spacing. Plant density is the goal, and you can get the same plant density with a narrow spacing as with a wide spacing by just slightly adjusting the seeding rate. To deal with competition from germinating weeds, consider wider spacings in no-till applications, and narrower spacings in harrowed fields.

The seeding rate for cover crops will generally be more than seeding rates for establishing forage crops because the goal is increased biomass and nitrogen production as well as weed suppression.

Living Mulch Intercropping

A living mulch is a cover crop that is intercropped with an annual or perennial cash crop, primarily for weed suppression and as a soil management practice. Living mulches reduce soil erosion, suppress weeds, increase soil organic matter, improve trafficability, increase water infiltration, and increase nutrient cycling. Legumes used as living mulches fix nitrogen from the air and can replace or reduce the need for nitrogen fertilizers. Some living mulches also provide habitat for beneficial insects.

Establishment Methods
There are three basic ways to establish a living mulch:

[1] drilling or broadcasting a cover crop together with the primary crop at planting;
[2] drilling (interseeding) or broadcasting (overseeding) a cover crop at the last cultivation;
[3] drilling a cash crop into mechanically suppressed strips of a living cover crop.

Living Mulch Systems and Methods of Suppression

When managed incorrectly, living mulches can act like weeds and compete with the main crop for light, water and nutrients. Especially in low-growing vegetables—such as vine crops—an overgrown living mulch can interfere with flowering and fruit development. Thus, management of a living mulch is geared to getting good ground coverage and then suppressing its growth through mechanical means.

The first 4 to 6 weeks after planting is the most critical growth period for most crops. During this time, plant competition can reduce yields most severely, and living mulch growth may require suppression. Using a method of suppression becomes most critical where soil moisture is limited. When a vegetable crop is planted directly into strips of live vegetation, methods of suppression prior to planting may include mowing, tillage, flaming, and a technique known as rolling (see Recourses below for more information).

When an intercrop is established at planting or by overseeding, methods of suppression may include time of establishment (in the case of overseeding), use of dwarf type cover crops, and light mechanical cultivation.

Dying Mulch/Living Mulch Weed Suppression

A dying mulch is a cover crop planted out of season that puts on some growth—suppressing weeds as a living mulch—and then dies back out on its own without requiring the use of herbicides, mowing, or tillage to knock it back. Winter rye—planted in the spring—has been used successfully in this manner in several agronomic and horticultural crops.

Here's how a dying mulch has been used by several Midwestern vegetable growers. In mid-spring, the field is overseeded with winter rye at 120 lbs. per acre to establish a living mulch. In order for winter rye to tiller and produce a seed head, it requires a period of cold treatment, or vernalization. Since it never receives vernalization and thus never tillers, it remains short and eventually just "cooks out" in summer, leaving a weed-suppressive duff.

The success of this system is dependent on proper timing and good luck. Timing is critical to get the rye established early enough to promote germination when the soil temperatures are still relatively cool, but at the same time, late enough that a cold spell is avoided. Since vernalization can occur when the rye is exposed to only 10 days of 45° F. night temperatures, a sudden spring cold snap can result in the cover crop performing in an other-than-expected manner.

Choice of Living Mulch Species

Cover crops, like any other crop, require fairly specific growing conditions. Both grasses and legumes are being used as living mulches. Of these, there are both cool season and warm season types to choose from.

Factors affecting choice of living mulch cover crop include the primary crop, rotation sequence, growing season, method of establishment, and intended use (i.e., dying mulch, winter killed mulch, etc.). Most important in the selection of a living mulch is that the plant species chosen be vigorous enough to provide the benefits of a cover crop, but not so vigorous that competition with the main crop cannot be managed without killing it. The region of the country (e.g., agroclimatic zone) is also of great importance in selecting a living mulch. For example, subterranean clover is grown as a winter annual legume in the South, but as a spring annual in the North.

Some grass species used as living mulches include perennial ryegrass, dwarf ryegrass, turf type fescues, millet, and out-of-season winter cereal grains. Some legume species used as living mulches include white clover, hairy vetch, subterranean clover, Dutch white clover, dwarf English trefoil, Korean lespedeza, and crimson clover. Broad-leaved cover crops that have potential as living mulches include phacelia, buckwheat, and various crucifers. Rapid cycling brassica germplasm is under development at the University of Minnesota. These are low-growing, short-season brassicas that function as smother crops early in the growing season, then mature early and leave a weed suppressive duff.

ATTRA's Overview of Cover Crops and Green Manures publication is a useful resource. It reviews the benefits and uses of cover crops and provides a number of useful resources on cover crops and seed sources.


Resources:

Alberta Agriculture. 1990. Alberta Forage Manual. Edmonton, Alberta.

Diver, S. 2007. Mechanical roller-crimper equipment used in no-till production. Fayetteville, AR: ATTRA Project. Contact ATTRA for a copy of this report.

Forage Information System. 2006. “Cover Crops.” Corvallis, OR: Oregon State University.

Grubinger, V. Cover Crops and Green Manures. University of Vermont Extension.

Posner, J. and T. Mulder. 2006. “Wisconsin Integrated Cropping Systems Trial Project.” Madison, WI: University of Wisconsin-Madison.

SAN. 2001. Managing Cover Crops Profitably, second edition.
Order hard copy at: Sustainable Agriculture Publications, PO Box 753, Waldorf, MD 20604-0753. (301) 374-9696

Singer, J. and P. Pedersen. 2005. Legume Living Mulches in Corn and Soybean. USDA-ARS National Soil Tilth Laboratory, Iowa State University.

Zemenchik, R.A., K.A. Albrecht, C.M. Boerboom, and J.G. Lauer. 2000. Corn Production with Kura Clover as a Living Mulch. Agron. J. 92:698–705.

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